1966 original Chevrolet 4 Speed

[GrumpysC10]

I have an original 4 speed in my 66 c10 but wondering if this transmission is worth keeping. The truck won't be raced, just cruised in and maybe jumped a little on the street (who doesn't like to jump on it at a light). Looking for any info or experience on it. Thanks.

[TJ's Chevy]

You have the SM420. Bullet proof and NOT a racing trans. Wide ratio gearing and a long throw makes for slow shifting. But they are a darn good tranny. I'd keep it.

[GrumpysC10]

Is it good for my application though? Sorry I am not good when it comes to transmissions.

[TJ's Chevy]

For what your doing I'd say it's fine. What kind of cruising are you doing? What engine do you have?

[GrumpysC10]

Car shows, around town, like I said just playing a little off the light. It has a 283. Not going crazy just a good motor.

[TJ's Chevy]

Yep, It'll be fine. And if your not happy, you can always do a swap later on. When my 66 is done I will be taking it to shows that are over 40 miles away. So I put in a 5 speed so I can easily cruise as free way speeds.

[GrumpysC10]

The shows I go to are freeway as well. My grandfather use to drive this truck all over.

[TJ's Chevy]

Originally Posted by GrumpysC10

The shows I go to are freeway as well. My grandfather use to drive this truck all over.

You might consider an OD tranny if your gonna be doing freeway. That or taller tires. I could do 60-65 with my 66 as it was. 292/sm420 3.73 gears and 30 inch tires. 283's are more of a high rpm v8 so it might be ok, But I would prefer to either put in taller gearing or an OD tranny if I was gonna be doing free way driving.

[jayoldschool]

"Playing a little off the light" will not be compatible with that trans. You'll never break it, but the ratios are all wrong for stoplight fun. It's a working truck trans. If you want to have fun, you need a car trans.

[oem4me]

My Suburban is 283/sm420 equipped. Not too much stop light fun to be had, unless you like creeping along in low gear at idle with your foot off the clutch.

[GrumpysC10]

What transmission would you recommend?

[jayoldschool]

Super T10
Muncie M20/21/22
T5
T56

[GrumpysC10]

What do they run used?

[TJ's Chevy]

Heck, I had plenty of fun with mine! Burn the tires off the line and shift to third! Anyhow, the other choices are good as well.

[GrumpysC10]

Originally Posted by TJ's Chevy

Heck, I had plenty of fun with mine! Burn the tires off the line and shift to third! Anyhow, the other choices are good as well.

You did that with the old four speed?

[TJ's Chevy]

Originally Posted by GrumpysC10

You did that with the old four speed?

Videos are worth a million words.

https://www.youtube.com/watch?v=ifh4eU5bUAo

In this video, the 1st was a rolling start. And the second pull I burned them off the line in 2nd then sifted to third. Motor didn't have enough torque to brake them loose again. But the slow shifting doesn't help either. I had lots of fun with it that way, but with my new setup...292/TKO600 5 speed it'll be even funner

https://www.youtube.com/watch?v=Nw_9eGLhhzk

[Chknlyps2]

Originally Posted by GrumpysC10

What do they run used?

Phoenix Craigslist has a couple Muncie's in the $200 range but 1 has a bad pic with the cover off and I can see a broken tooth on a gear right off the bat. Decent ones are in the $600 to $800 range but then you still need shifter, clutch and possibly bellhousing because the opening from your SM420 might be bigger, I know an SM465 has a bigger register opening.

Your SM420, any car 4 speed manual like the Muncie, a T10, a 3 on the tree manual 3 speed, or a 3 speed automatic like a Turbo 350 or 400 all have a 1 to 1 final drive ratio. Meaning that in high gear, when your motor is turning 2,500 RPM so is your driveshaft. They will all feel the same and your motor will turn the same RPM when you are in high gear going down the freeway at 65 MPH

My 64 with a 283, 4.56 gears, 31 1/2 inch tall tires and a 3 on the tree turns almost 3,000 RPM doing 60 and it sounds wound out! If I went to an over drive trans like an NV4500 (still a truck trans) T5, 700R4 etc I could drop that RPM down to 2,100 to 2,300. In this day and age with over drive trannys we are use to only hearing that 3,000 RPM when we are on it going through the gears or stepping on it to pass.

You will have to do some research, There are T5's from Camaro's but the shifter placement is farther back than ones from S10's and bench seats get in the way. Most have electronic speed sensors, a few early years have mechanical speedo drives.

[GrumpysC10]

Which transmission would be best for shifter placement or am I going to have to cut the floor?

[TwoFiftyShifter]

Any other tranny will probably be longer than the SM420 - you will need to cut a hole for it I believe.